1. Field of the Invention
This invention relates to a laser range finder, and more particularly, to a laser range finder which measures the range of a target by measuring the time it takes for a laser light to be reflected from the target.
2. Description of the Prior Art
The structure of a typically conventional laser range finder is shown in FIG. 1 which has been presented herein for the purpose of distinguishing the improvement in the invention in detail. The conventional laser range finder is designed so as to employ two light sources, namely, a light emitting diode (LED 30) for collimating a target, and an infrared ray laser 10 to measure the distance between the target and the viewer's eye.
The light emitted from the LED 30 is converted to parallel light and then reflected on a third beam splitter 12, followed by an expansion through a beam expander composed of a first lens 14 and a second lens 16.
Thereafter, the light passes through a first beam splitter 18 and is then reflected on a corner cube 20. The light thus reflected is then retro-reflected by the splitter 18 and entered, via a telescope 24, the viewer's eye 26.
A front surface 18A of the first beam splitter 18 is coated with a dielectric material so that the surface 18A can induce a full reflection by the infrared ray and a partial reflection by the visible light. A rear surface 18B of the splitter 18 is anti-reflection coated for visible light. Since the beam splitter 18 is inclined at a 45.degree. angle to the optical axis, the light emitted from the laser 10 is reflected on the first beam splitter 18 and directed toward a target 22. Then, after the light is reflected from the target 22, it is reflected on a second beam splitter 32 and then entered into a detector 34.
With the conventional laser range finder as described hereinabove, it is possible to measure an accurate distance only when the positions of the third lens 28 and the third beam splitter 12 are constantly maintained. However, the conventional laser range finder has the disadvantage that when the positions of the third lens 28 and/or the third beam splitter 12 are altered and shifted during moving, or due to a vibration and/or a shock, the traveling direction of the light of the LED differs from that of the laser resulting in the occurrence of errors in the measurement of the distance; thus, it is difficult to obtain an accurate measurement of the distance. PG,4